Conventionally, there are provided tightening tools such as torque wrenches equipped with an electronic circuit, by which in tightening a member to be tightened such as a bolt, when a tightening torque has reached a set torque value, data of a tightening torque value and the like is wirelessly transmitted to indicate the end of tightening of the member to be tightened (Patent Literature 1).
Such tightening tools are provided with a power supply battery (battery) in an exchangeable manner to supply electric power to an electronic circuit including a wireless transmitter.
When the battery is employed as a power source of the tightening tool, if the use of the tightening tool is started with a low remaining battery level, the use might be continued without being noticed of battery exhaustion during the use. In this case, no tightening data is transmitted.
The battery exhaustion or the low remaining battery level requires an exchange operation of batteries, or a connection operation of a charging cable for recharging. Such operations are performed as part of daily maintenance, for example, in machine assembly plants and the like.
On the other hand, the tightening tools of a battery exchange type need a battery contact and hence easily have a contact failure, and specifically the torque wrenches tend to have a defective battery contact or the like due to a large impact applied thereon during use. The tightening tools having a rechargeable battery as a power supply cannot avoid a break of a charging jack and a break of the charging cable.
Thus, daily maintenance management is important for the tightening tools with the battery as the power supply part.
On the other hand, there are provided many products of tools such as torque wrenches equipped with an electronic circuit. A dry cell is generally used as a power supply for such an electronic circuit, but the products using a solar cell are proposed (Patent Literature 2).
In attaching the solar cell to the tool (hereinafter called tool with the solar cell), for example, a torque wrench, it should be considered that the solar cell does not interfere with operation of the tool such as a torque wrench, and a light receiving surface can receive as much light as possible, and the like.
The tool with the solar cell is often put on a workbench or the like during standby in a tightening operation, for example. An operator puts the tool on the workbench with confirmation that the light receiving surface of the solar cell faces toward room light, so that electric power generated by the solar cell that has received light of, for example, a ceiling light can be accumulated in a storage battery for that duration.
However, when the operator puts the tool with the solar cell in a hurry without being sure whether or not the light receiving surface of the solar cell faces upward, the tool may be put such that the light receiving surface of the solar cell faces to the workbench and no light arrives at the light receiving surface of the solar cell.